The registry package provides a general set of operations for
manipulating the Windows registry. The package implements the
registry Tcl command. This command is only supported on the
Windows platform. Warning: this command should be used with caution
as a corrupted registry can leave your system in an unusable state.

KeyName is the name of a registry key. Registry keys must be
one of the following forms:

\\hostname\rootname\keypath

rootname\keypath

rootname

Hostname specifies the name of any valid Windows
host that exports its registry. The rootname component must be
one of HKEY_LOCAL_MACHINE, HKEY_USERS,
HKEY_CLASSES_ROOT, HKEY_CURRENT_USER,
HKEY_CURRENT_CONFIG, HKEY_PERFORMANCE_DATA, or
HKEY_DYN_DATA. The keypath can be one or more
registry key names separated by backslash (\) characters.

The optional -mode argument indicates which registry to work
with; when it is -32bit the 32-bit registry will be used, and
when it is -64bit the 64-bit registry will be used. If this
argument is omitted, the system's default registry will be the subject
of the requested operation.

Option indicates what to do with the registry key name. Any
unique abbreviation for option is acceptable. The valid options
are:

Sends a broadcast message to the system and running programs to notify them
of certain updates. This is necessary to propagate changes to key registry
keys like Environment. The timeout specifies the amount of time, in
milliseconds, to wait for applications to respond to the broadcast message.
It defaults to 3000. The following example demonstrates how to add a path
to the global Environment and notify applications of the change without
requiring a logoff/logon step (assumes admin privileges):

If the optional valueName argument is present, the specified
value under keyName will be deleted from the registry. If the
optional valueName is omitted, the specified key and any subkeys
or values beneath it in the registry hierarchy will be deleted. If
the key could not be deleted then an error is generated. If the key
did not exist, the command has no effect.

Returns the data associated with the value valueName under the key
keyName. If either the key or the value does not exist, then an
error is generated. For more details on the format of the returned
data, see SUPPORTED TYPES, below.

If pattern is not specified, returns a list of names of all the
subkeys of keyName. If pattern is specified, only those
names matching pattern are returned. Matching is determined
using the same rules as for string match. If the
specified keyName does not exist, then an error is generated.

If valueName is not specified, creates the key keyName if
it does not already exist. If valueName is specified, creates
the key keyName and value valueName if necessary. The
contents of valueName are set to data with the type
indicated by type. If type is not specified, the type
sz is assumed. For more details on the data and type arguments,
see SUPPORTED TYPES below.

If pattern is not specified, returns a list of names of all the
values of keyName. If pattern is specified, only those
names matching pattern are returned. Matching is determined
using the same rules as for string match.

Each value under a key in the registry contains some data of a
particular type in a type-specific representation. The registry
command converts between this internal representation and one that can
be manipulated by Tcl scripts. In most cases, the data is simply
returned as a Tcl string. The type indicates the intended use for the
data, but does not actually change the representation. For some
types, the registry command returns the data in a different form to
make it easier to manipulate. The following types are recognized by the
registry command:

The registry value contains a null-terminated string that contains
unexpanded references to environment variables in the normal Windows
style (for example,
“%PATH%”).
The data is represented in Tcl as a string.

The registry value contains a device-driver resource list. The data
is represented exactly in Tcl, including any embedded nulls.

In addition to the symbolically named types listed above, unknown
types are identified using a 32-bit integer that corresponds to the
type code returned by the system interfaces. In this case, the data
is represented exactly in Tcl, including any embedded nulls.

Print out how double-clicking on a Tcl script file will invoke a Tcl
interpreter:

package require registry
set ext .tcl
# Read the type name
set type [registry get HKEY_CLASSES_ROOT\\$ext {}]
# Work out where to look for the command
set path HKEY_CLASSES_ROOT\\$type\\Shell\\Open\\command
# Read the command!
set command [registry get $path {}]
puts "$ext opens with $command"